Curing epoxide resin with boron trichloride-amine complex

ABSTRACT

CURABLE COMPOSITIONS COMPRISES AN EPOXIDE RESIN AND A COMPLEX OF FORMULA BCL3.NR4R5R6 WHERE R4, R5 AND R6 TOGETHER WITH THE NITROGEN ATOM FORM A HETEROCYCLIC RING, OR R4 AND R5 BOTH REPRESENT METHYL GROUPS AND R6 DENOTES AN ALKYL OR ARALKYL GROUP OF AT LEAST 6 AND AT MOST 18 CARBON ATOMS. PREFFERED COMPOSITIONS CONTAIN COMPLEXES IN WHICH NR4R5R6 DENOTES PYRIDINE, AND THOSE IN WHICH R6 DENOTES AN ALKYL HYDROCARBON GROUP OF 6-18 CARBON ATOMS OR A BENZYL GROUP. THE COMPLEXES ACT AS LATENT HARDNESS.

United States Patent @ffice 3,784,647

Patented Jan. 8, 1974 3,784,647 trichlorifle with tertiary amins, viz. complexes formed CURING EPOXIDE RESIN WITH BORON ammes fmmula rRrcHLoRrnE-mvmsn COMPLEX RB George Latto Fleming, Salfron Walden, and Richard John 1 i; 3

Martin, Linton En land assi ors to Ciha-Gei AG Basel Switzerkmd g gn gy 5 where R R and R are alkyl groups containing from 1 N D i Filed A 9, 1971, s 170 3 to 4 carbon atoms. Mixtures of epoxide resins with such Claims priority, application Great Britain, Aug. 11, 1970, complexes are said to have exceptionally long pot-lives at 38,647/70 elevated temperature, relatively short curing times at Int. Cl. C08g 45/06 US Cl 260 g30 TW 9 Claims 10 curing temperatures, mg storage-life, and relatively high hydrolytic stability. The use of boron trichloride-trimethylamine complex, and its advantages over a known curing ABSTRACT OF THE DISCLOSURE ageltt, 1130 55? trifluoridgc-lmolrxloetahylamine, are described t a s t at oron trichloride-trieth 1- Curable composltrons comprise an epox1de res1n and m 31 1S paten y a complex of formula BCl -NR R R where R, R and 1 gifi g jg evaluated and had Substannany ii; t a iiii R l: t l i autml i a g gg Unpublished experiments by the applicants have shown, g an al y 1 f z gfi g z p g g s i g 3 at however, that the boron trichloride-triethylamine complex m s 8 ar atomsbehaved quite differently from the trimethylamine comlex and was not latent to an appreciable extent Preferred com osltrons contaln com lexes 1n whrch p NR R R denotes pyridine and those in v vhich R denotes 2 2 borgn ig i i ig' g g t was fi t pare rom ry rie y amine g. an oron tric o- Iarelnaztilliyglrgggrocarbon group of 6 18 Carbon atoms or a ride (42 g.) in n-pentane. The reactants were combined at -78 C. under nitrogen and the reaction mixture was The complexes act as latent hardeners allowed to warm to room temperature. The buff-coloured precipitate was recrystallised from ethanol to give white This invention relates to curable epoxide resin com- Crystals 0f the complex melting at C and having the positions and to the products obtained by curing such following elemental analysis: 339%; H, compositions. 6.4%; C H N.BCl requires C, 33.0%; H, 6.9%; N,

It is known that epoxide resins, i.e. substances containing on average more than one 1,2-epoxide group per In contrast to the trimethylamine-boron trichloride commolecule, may be cured, i.e. hardened, on reaction with P P p as described in various classes of substances to form products having the triethylamine complex Was found to be hygroscopic.

valuable technical properties. With one class of curing The following comparative tests were carried out.

agents, such as the alkylene polyarnines, application of (a) Samples of boron trichloride-trimethylamine and heat is usually unnecessary. With a second class, the so- -triethylamine complexes were added to a solvent-free called heat-curing agents, it is necessary to apply heat so liqu d p lygly i yl ether of ,2- (4- y yph yUp that cross-linking is substantially complete within a conpane, having an epoxide content of 5.0 to 5.2 equivalents veniently short time. Representative of this second class per kilogram, so that the complex content was 3 parts are polycarboxylic acids and their anhydrides, aromatic per 100 parts of resin. The mixtures were stored at 40 polyamines, polycarboxylic acid polyhydrazides, and di- C. The mixture containing the triethylamine complex had cyandiamide. gelled after 3 weeks whereas that containing the trimethyl- There is a demand for latent curing agents, i.e. subamine complex was still ungelled after 9 months.

stances which are substantially inert towards the epoxide (b) Samples were mixed with the same epoxide resin and the gel times were measured at various temperatures. The results were as follows:

resin at room temperature (thus permitting the resin and B cl trimethylamine B C1 .triethylamine prolonged periods), and also at moderate temperatures, These results show that whilst there is a marked transisay 40 C., so that the pot-life is reasonably long, yet tion in gel times for the trimethylamine complex between which, at curing temperatures, effect rapid cross-linking. 100 and 130 C., the triethylamine complex does not Several types f la u i g g t have been gg show such a transition in properties. Therefore, the tribut those hitherto available have proved in practice not ethylamine complex cannot b classed as a latent hardto fulfill all the requirements. Some are insufliciently latent, ener, Whereas the trimethylaminfi complex is clearly reacting with the resin at room temperature to an extent latent that g s fif gf g i fi Other complexes of boron trichloride examined by the agen are 00 S or W 16 n mac mg 0 a y applicants and found not to be latent included those appreciable extent with the resin at room temperature, eiiect curing on heating so slowly as to require inconfgggi g g g' and NN'dlmethyl' veniently long curing times. Yet others have further disadvantages, e.g. the mixture of curing agent and resin is Hence, it was not obvious to those ekilled the aft too sensitive to moisture, or the electrical properties of the that eempleXes of boron hlehloflde h certaln other cured resin are poor. tertiary amines would be useful latent curing agents. Sur- Recently, it ha been proposed (US, Pat. No, 3,395,- prisingly, it has been found that complexes with certain 121) to use as curing agents certain complexes of boron heterocyclic, araliphatic, and higher alkyl tertiary amines do behave as curing agents with a very high degree of latency.

The present invention accordingly provides curable compositions comprising: (1) an epoxide resin, and (2) a complex of formula BCl .NR R R wherein R R and R together with the indicated nitrogen atom, represent a 5- or 6-membered heterocyclic ring which may be substituted by a lower alkyl group containing 14 carbon atoms, or R and R both represent methyl groups and R denotes an alkyl or aralkyl group of at least 6 and at most 18 carbon atoms.

The preferred complexes are those in which R R and R together with the indicated nitrogen atom, denote pyridine, and those in which R denotes either an alkyl hydrocarbon group of at least 6 and at most 18 carbon atoms or a benzyl group. The complex with pyridine is known (see Bax et al., J. Chem. Soc., 1958, 1254): the other preferred complexes are believed to be new.

Epoxide resins which may be employed in these compositions are in general those containing terminal groups of formula where R denotes a hydrogen atom or a methyl group, particularly as 2,3-epoxypropyl groups directly attached to oxygen, nitrogen or sulphur atoms.

As examples of such resins may be mentioned polyglycidyl and poly(fl-methylglycidyl) esters obtainable by reaction of a compound containing two or more free carboxyl groups per molecule with epichlorhydrin, glycerol dichlorohydrin, or fi-methylepichlorohydrin in the presence of an alkali. Such polyglycidyl esters may be derived from aliphatic polycarboxylic acids, e.g. oxalic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and dimerized or trimerized linoleic acid; from cycloaliphatic polycarboxylic acids such as tetrahydrophthalic acid, 4-methyltetrahydrophthalic acid, hexahydrophthalic acid, and 4-methylhexahydrophthalic acid; and from aromatic polycarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid.

Further examples are polyglycidyl and poly(B-methylglycidyl) ethers obtainable by reaction of a compound containing at least two free alcoholic hydroxyl and/or phenolic hydroxyl groups per molecule with the appropriate epichlorohydrin or glycerol dichlorohydrin under alkaline conditions or, alternatively, in the presence of an acidic catalyst and subsequent treatment with alkali. These ethers may be derived from acyclic alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, and higher polyoxyethylene glycols, propane-1,2-diol and polyoxypropylene glycols, propane-1,3-diol, butane-1,4- diol, polyoxybutylene glycols, pentane-l,5-diol, hexane- 1,6-diol, hexane-2,4,6-triol, glycerol, 1,1,1-trimethylolpropane, pentaerythritol, or poly(epichlorohydrin); from cycloaliphatic alcohols such as resorcitol, quinitol, bis(4- hydroxycyclohexyl methane, 2,2-bis (hydroxycyclohexyl) propane, and 1,l-bis(hydroxymethyl)cyclohex-3-ene; and from alcohols having aromatic nuclei, such as N,N-bis (2-hydroxyethyl)aniline and ,p-bis(Z-hydroxyethylamino)diphenylmethane. Or they may be derived from mononuclear phenols, such as resorcinol and hydroquinone, and polynuclear phenols, such as bis(4-hydroxyphenyl)methane, bis(4-hydroxyphenyl) sulphone, 1,1,2,2- tetrakis(4 hydroxyphenyl) ethane, 2,2 bis( 4 hydroxyphenyl) propane (otherwise known as bisphenol A), 2,2- bis(3,S-dibromo-4-hydroxyphenyl)propane, and novolaks formed from aldehydes such as formaldehyde, acetaldehyde, chloral, or furfuraldehyde, with phenols such as phenol itself, and phenol substituted in the ring by chlorine atoms or by alkyl groups each containing up to eight carbon atoms, such as 4-chlorophenol, Z-methylphenol, and 4-te1 t.butylphenol.

Poly(N-glycidyl) compounds include, for example, those obtained by dehydrochlorination of the reaction products of epichlorohydrin with amines containing at least two amino-hydrogen atoms such as aniline, n-butylamine, bis(4-aminophenyl)methane, or bis(4 methylaminophenyl)methane; triglycidyl isocyanurate; and N,N- diglycidyl derivatives of cyclic ureas such as ethyleneurea or 1,3-propylene urea and hydantoins such as 5,5- dimethylhydantoin.

Examples of poly(S-glycidyl) compounds are di-& glycidyl derivatives of dithiols such as ethane-1,2-dithiol and bis(4-mercaptomethylphenyl ether.

Epoxide resins having terminal 1,2-epoxide groups attached to different kinds of hetero atoms may be employed, e.g. the N,N,'O-triglycidyl derivative of p-aminophenol, or glycidyl ether-glycidyl esters of salicylic acid or phenolphthalein.

If desired, a mixture of epoxide resins may be used.

The curing agents of this invention are particularly useful when employed with polyglycidyl ethers of polyhydric phenols; especially suitable resins are polyglycidyl ethers of 2,2-bis (4-hydroxyphenyl)propane or of a novolak formed from formaldehyde and phenol, or phenol substituted in the ring by one chlorine atom or by one alkyl hydrocarbon group containing from one to eight carbon atoms, and having an epoxide content of more than about 0.5 1,2-epoxide equivalent per kilogram.

The curing agents of the present invention need not be used alone but may, if desired, be used in admixture with other known curing agents for epoxide resins, such as polycarboxylic acids and their anhydrides, and amines.

The proportion of curing agent to be used will depend on such factors as the epoxide content of the epoxide resin used, the nature of the curing agent, and the curing conditions to be employed. The proportion required may be readily determined by routine experimentation but, by way of illustration, from about 0.1 to 10, and especially about 1 to 5, parts by weight of the curing agent may be used per parts by Weight of the epoxide resin.

The new compositions may further contain suitable plasticizers such as dibutyl phthalate, dioctyl phthalate or tricresyl phosphate, inert diluents, and so-called reactive diluents, such as furfuryl alcohol and especially monoepoxides, for example, butyl glycidyl ether, iso-octyl glycidyl ether, phenyl glycidyl ether, or glycidyl esters of synthetic, highly branched, predominantly tertiary, aliphatic monocarboxylic acids. They may also contain additives such as fillers, reinforcing materials, colouring matter, flow control agents, flame inhibitors, mould lubricants, and the like. Suitable extenders, fillers and reinforcing materials are, for example, asphalt, bitumen, glass fibres, carbon fibres, mica, quartz flour, cellulose, kaolin, wollastonite, colloidal silica having a large specific surface, e.g. that available under the registered trademark Aerosil, powdered poly(vinyl chloride) or powdered polyolefin hydrocarbons.

The curable compositions of this invention may be used as laminating resins, paints and lacquers, sinter powders, impregnating and casting resins, moulding compositions, hot-curing putties and sealing compounds, potting and insulating compounds for the electrical industry, and adhesives, and also in the manufacture of such products.

The following examples illustrate the invention. Unless otherwise specified, parts are by weight. Infusibility times were determined by placing a sample of the composition on a surface maintained at the test temperature shown: at intervals, small portions of the sample were removed and checked for fusibility by placing them on a surface at 250 C. The duration of heating required at the test temperature to render the sample infusible was noted as the infusibility time.

Epoxide resin I denotes a polyglycidyl ether of 2,2- complex (84.9 g.), M.P. 28 C. The product had the elebis(4-hydroxyphenyl)propane, having a 1,2-epoxide conmental analysis: C, 44.05%; H, 8.48%; N, 5.10%. tent of 5.16 equivalents per kilogram and a viscosity at CmHggN-BC13 requires C, 43.74%; H, 8.38%; N, 5.10%. 21 C. of 245 poises. This product is hereinafter referred to as Complex B.

Epoxide resin II denotes a polyglycidyl ether of a 5 Boron trichloride-pyridine complex was prepared as phenol novolak resin, having a 1,2-epoxide content of follows:

5.45 equivalents per kilogram, and a softening point of Boron trichloride (72 g.) was bubbled through dry 35 C. pyridine (49 g.) in benzene at 0 C. in an atmosphere P resin denotes a Solid p lyg y i yl ether of nitrogen. On completing the addition, the mixture was of 2,2-bis(4-hydroxyphenyl)propane, havinga 1,2-epoxide stirred for 3 hours at 0 C. The precipitated white solid content of 1.97 equivalents per kilogram. was recrystallized from ethanol and dried to give boron p resin V" denotes a p y ycid l ether of trichloride-pyridine complex 118 g.), M.P. 114 c. having a Poxide content of 8.85 Elemental analysis gave the results: C, 30.05%;H, 2.38%;

equivalents per kilogram. N, 6.91%. C H N.BCl requires C, 30.56%; H, 2.55%;

Epoxi'de resin V denotes an adduct resin prepared by N, 7.13%. This product is hereinafter referred to as heating for 2 hours at 120 C. (a) 100 parts of a poly- Complex C. glycidyl tetrahydrophthalate, having a 1,2-epoxide content EXAMPLE 1 of 6.35 equivalents per kilogram, and (b) 50 parts of an I acid-terminated polyester prepared from adipic acid (8 C P Q B and C Q mlXed Wlth Samples of moles), insophthalic acid (2.8 moles) and propane-1,2- Epoxide Teslh I the PTOPOTUOII P 3 t0 5 P P 100 diol (9.8 moles); having an acid content of 1.49 equiva- Parts Of the reslll- For cohlpar'lhve P P a known lents per kilogram. Thus prepared, Epoxide resin V had latent f boron iflfiuofldefethylahllhq Complex, a 1,2-epoxide content of 4.05 equivalents per kilogram Was mlXed with a Sample of Epoxlde 176511} I 111 the P and a viscosity of 130 poises at C. portion of 3 parts per 100 parts of the resin.

Epoxide resin VI denotes the tetrakis(N-glycidyl) 25 Viscosity measurements were taken of all samples over derivative of bis(4-aminophenyl)methane having a 1,2- 2. period at 21 C. and at C. The results are given epoxide content of 8.2 equivalents per kilogram. in Table I.

TABLE I Hardener Initial viscosity at 21 C. (poises) 760 275 275 215 185 245 Time taken to double initial viscosity at 21 0.

(weeks) 6 17 17 17 17 14 Viscosity after 8 Weeks at 21 C. (poises) 2, 200 270 317 250 225 322 Initial viscosity at 40 C. (poises) 55 24 23 20 17 22 Time taken to double initial viscosity at 0 (weeks) 1 9 6. 7 17 17 4 Boron trichloride-N-benzyldimethylamine complex was The results show that the mixtures containing Comprepared as follows. plexes A, B, and C were much slower to cure at 21 C.

Dry benzyldimethylamine (125 g.) was stirred at 0 and 40 C. than that containing the boron trifluoridein dry benzene in an atmosphere f nitrogen Boron ethylamine complex: pot-lives of such mixtures would trichloride (108 g.) in dry benzene was added slowly. On therefore be much longerthe addition being completed, the mixture was stirred for EXAMPLE 2 3 hours at 0 C., then the precipitated solid was recrystalcomplexes A, B, and C were mixed With Epoxide resin lized from ethanol and dried to give white crystals of I as described in Example 1 and the d fl ti tempera b ron trichlorideen yl im y complex tures under load (D.T.L.) were measured for the cured M.P. 131 C. The product had the analysis: C, 42.14%; samples in accordance with British Standard 2782, Meth- H, 4.97%; N, 5.55%. C H N.BCl requires C, 42.81%; 0d 1026. The results are given in Table II.

TABLE II Hardener D.T.L. after cure cycle BFaCzHsNHz Complex A Complex B Complex 0 1 Still liquid. H, 4.96%; N, 5.34%. This product is hereinafter referred These results show that a more rapid rate of cure can to as Complex A. be obtained with Complex B than with BF eethylamine Boron trichloride-octyldimethylamine complex was precomplex at 120 C., despite the longer pot life of the pared as follows: former system (Table 1). Further, although the BF com- Empigen 5015 (a commercial mixture of n-alkyldiplex gives a higher D.T.L. than the BCl complexes after methylamines in which n-octyldimethylamine predomithe exhaustive cure (schedule C), after heat-ageing nates) (120 g.) was stirred in an atmosphere of nitrogen (schedule D) this advantage is lost. at 30 to 40 C. whilst boron trichloride (87 g. was slowly bubbled through the mixture. A brown crude product was EXAMPLE 3 obtained which, on recrystallization from ethanol, gave The mixtures described in Example 1 were tested acwhite crystals of boron trichlorideoctyldimethylamine cording to British Standard 2782, Method 205D for power factor, tan 6, at 50 Hz. and method 206D for tan 6, at 1 kHz. The results are given in Table III.

B (3 parts). The composition showed no significant change of viscosity after storage at 40 C. for 1 month, but

TABLE III Hardner BFa-CzHBNHz Complex A Complex B Complex Amount (parts per 100 of resin) Power factor (tan 6) at 50 Hz. and 110 C. after a cure at 120 C. of-

3 hours 0. 1 A 0. 028 8 hours. 0.1 0. 014 0.013 16 hours 0. 1 0. 039 0. 042 Power factor (tan 6) at 1 kHz. and 160 C. after a cure of- 2 hours at 120 0. plus. 6 hours at 150 0. plus. 0. 078 0.018 0. 040 0.012 0. 043 0.018 2 hours at 190 C The superiority of the mixtures containing Complexes A, B, and C in respect of power factor-temperature characteristics is clearly demonstrated by the above results. The rapid rate of cure noted in Example 2 with 5% of Complex B is further reflected in the low power factor of the specimen cured at 120 C. for 3 hours.

EXAMPLE 4 A composition suitable for pre-impregnating glasscloth or mica-tape was prepared by mixing a solution of Epoxide resin II (100 parts), acetone parts), Complex B (5 parts), and toluene (5 parts). The viscosity of this solution was determined when freshly prepared and after storage for 8 weeks at 40 C. During this period the viscosity rose from 0.84 poise to 1.00 poise. After storage, the solvent was removed at 100 C. under vacuum and tests were carried out on the distillate and the residual resin-hardener mixture.

The ultraviolet spectrum of the solvent showed complete absence of phorone, demonstrating that, unlike boron trifluoride-ethylamine complex, Complex B does not catalyze acetone-condensation reactions.

The residual resin hardener mixture was compared with the equivalent material obtained from the unaged solution. The results are shown in Table IV.

as above).

It is clear from the above results that the resin hardener mixture is storage stable at 40 C. even in acetone solution: similar compositions in which boron trifluoride complex hardeners are used are, however, not storage-stable.

EXAMPLE 5 A mixture of Epoxide resin III (60 parts), Epoxide resin IV (40 parts), and Complex B (3 parts) was prepared by heating and stirring the two resins at 120 C., then cooling to 40 C. and mixing in the Complex B.

The composition obtained showed no significant change of viscosity after storage at 40 C. for 1 month, but cured almost completely after heating for 4 hours at 135 C. The cured product was flexible, had an excellent shock resistance, and had a high impact strength. The impact strength, determined in accordance with British Standard 2782 Method 306A, was 1.5 ft.-lbf. (metric equivalent 0.2 m.-kgf.). The product showed good retention of flexibility on heat ageing at 150 C.

EXAMPLE 6 Epoxide resin V (100 parts) was mixed with Complex cured almost completely within 2 hours at 120 C. The cured product was tough and flexible, and had good thermal shock resistance.

EXAMPLE 7 This example demonstrates the higher reactivity of Complex B compared with boron trichloride-trimethylamine complex.

Epoxy resin I (100 parts) was mixed with BCl -trimethylamine complex (3 parts) and with Complex B (3 parts). These compositions, both of which contain the same molar proportion of BCl -complex, were compared for stability at 40 C. and reactivity at 120 C. The

It is evident from Table V that whilst both BCl -trimethylamine and BCl -octyldimethylamine give adequate stability at 40 C., the latter complex produces substantially faster cure at 90120 C.

EXAMPLE 8 Complex B was mixed with a sample of Epoxide resin VI in the proportion 5 parts per parts of resin, and the deflection temperature under load (D.T.L.) was measured for the cured samples in accordance with British Standard 2782, Method 1026. A sample cured at C. for 2 hours had a D.T.L. of 85 C., and a sample cured at 135 C. for 2 hours, followed by C. for 2 hours, had a D.T.L. of 191 C.

What is claimed is:

1. A curable composition comprising:

( 1) an epoxide resin containing on average more than one 1,2-epoxide group per molecule, and (2) a curing amount of a complex of formula where R and R each denote a methyl group and R denotes a group having at least 6 and at most 18 carbon atoms and is selected from the class consisting of alkyl groups and aralkyl groups.

2. A composition according to claim 1, in which R denotes a group selected from the class consisting of alkyl hydrocarbon groups and benzyl groups.

3. A curable composition comprising:

(1) an epoxide resin containing on average more than one 1,2-epoxide group per molecule, and (2) a curing amount of a complex of formula BC1 NR R R where R R and R together with the indicated nitrogen atom, represent a heteroeyclic ring selected from the class consisting of mononuclear heterocyclic rings containing at least and at most 6 members in the ring and mononuclear heterocyclic rings containing at least 5 and at most 6 members in the ring and substituted in the ring by an alkyl group of not more than 4 carbon atoms.

4. A composition according to claim 3, in which NR R R denotes pyridine.

5. A composition according to claim 1, in which the Epoxide resin (I) contains groups of the formula where R is a substituent selected from the class consisting of hydrogen atoms and methyl groups.

6. A composition according to claim 5, in which the epoxide resin contains 2,3-epoxypropyl groups directly attached to heteroatoms selected from the class consisting of oxygen, nitrogen, and sulphur atoms.

7. A composition according to claim 3, in which the Epoxide resin (I) contains groups of the formula where R' is a substituent selected from the class consisting of hydrogen atoms and methyl groups.

8. A composition according to claim 7, in which the epoxide resin contains 2,3-epoxypropyl groups directly attached to heteroatoms selected from the class consisting of oxygen, nitrogen, and sulphur atoms.

9. The heat-cured product of the composition of claim 1.

References Cited UNITED STATES PATENTS 3,395,121 7/1968 Pfann et a1. 260-47 2,824,083 2/1958 Parry 260-47 WILLIAM H. SHORT, Primary Examiner T. PERTILLA, Assistant Examiner US. Cl. X.R.

1l7--l24 E; 161-184; 260-2 N, 9, 30.4 EP, 28, 30.6 R, 31.8 E, 37 EP, 47 EN, 59, EP, 77.5 NC, 78.4 EP, 79, 836 

